Larry Weise, age 12, of Tuscon, Arizona, for his question:

Which is the softest mineral?

The experts have graded the earth’s minerals in order of their hardness. There are ten classes of mineral hardness, the hardest being class tens the softest class one. Class ten belongs to the diamond, hard enough to scratch any other natural mineral. No other natural mineral can scratch it back.

The softest mineral is talc, a soapy stone, soft enough to be scratched with the fingernail. The soft mineral called soapstone, used to make figurines, is composed mostly of talc. Quantities of talc are used to make talcum powder, cosmetics, paints and ceramics.

Soft talc stone is composed of magnesium, silica and water. It is classed as a metamorphic, or made‑over, rock. A slab of talc breaks easily into leafy flakes. The flakes may be silvery grey, whitish green, or they may glow with a pearly lustre. In the earth, this softest of all minerals occurs as a greyish stone. It feels soapy or greasy to the touch. The United States mines and uses more talc than any other country in the world.